A Planar and a Volumetric Test for Stereoanomaly

Abstract

Stereoanomaly is the failure to see differences in depth when the viewer is presented with stimuli having different magnitudes of stereoscopic disparity. In the absence of eye movements, everyone suffers from stereoanomaly for extremely large disparities. Typically, such disparities are seen at the same depth as monocular stimuli. However, about 30%, of the population exhibit some form of stereoanomaly even for very small disparities, provided eye movements are avoided. In some cases, the sign of the disparity will be confused, and the perceived depth will be incorrectly seen as 'behind' rather than 'in front of' the fixation point, for example. Because anomalies provide useful information about perceptual mechanisms, tests that measure and quantify the extent of a blindness are important investigative tools for research. Here we offer two easy-to-administer tests for stereoanomaly. The first test is based on depth judgments of two bars relative to a fixation point. The second test involves judgments of volumetric stimuli, seen stereoscopically. In each case, subjects indicate depth by setting a rectangle (with fixed base) to match the perceived depth. Although both tests are correlated, some differences in stereo processing are seen, depending upon whether or not the stimuli are presented near the point of fixation.

Voluntarily controlled bi–stable slant perception of real and photographed surfaces

“…For example, in the current study, two subjects (GK and SP) were able to experience mono stability only when disparity and perspective specified identical slants, whereas for the other subjects those slants needed to be only of the same sign to produce this experience (see figure 5). It is interesting to relate the differences between subjects to stereo-anomaly (Harwerth et al 1998;van Ee & Richards 2002). Five of our subjects (NK, MS, RR, SV and TV) were excellent at distinguishing the signs and magnitudes of both the crossed and the uncrossed disparities.…”

“…Their stereo vision was tested by a stereo-anomaly test of the ability to distinguish between crossed and uncrossed disparities (defined relative to the monitor) of magnitudes within a range of À1 to 1 , without the possibility that eye movements interfere (van Ee & Richards 2002). Subjects NK, MS and SV were excellent at distinguishing the signs and magnitudes of both the crossed and the uncrossed disparities.…”

How to use individual differences to isolate functional organization, biology, and utility of visual functions; with illustrative proposals for stereopsis

“…Such methods have also contributed to our knowledge of the functional organization of color vision (Bimler, Kirkland & Jameson, 2004;Gunther & Dobkins, 2003;Burt, 1949;Jones, 1948) and motion perception (Morrone et al, 1999). In addition, individual differences based studies have yielded insights into the functional organization of color vision (Malkoc et al, 2005;Webster et al, 2000aWebster et al, ,b, 2002Pickford, 1951), stereopsis (van Ee & Richards, 2002;van Ee, 2003;Scharff, 1997;Regan et al, 1986;Richards & Lieberman, 1985;Richards & Regan, 1973), and shape from shading (Adams, 2007) without explicitly using latent variable models. While the studies mentioned above test specific hypotheses of functional organization, an approach referred to as "confirmatory," individual differences based techniques are also valuable for so-called "exploratory" analysis when no such hypotheses exist (Thurstone, 1947(Thurstone, , 1944.…”

Multivoxel Pattern Selectivity for Perceptually Relevant Binocular Disparities in the Human Brain

“…Mean age was 26.7 years (range, 20 -42 years). All observers had normal or correctedto-normal vision and were screened for stereo deficits using a dynamic stereo test (van Ee and Richards, 2002). All stimuli presented in the study were above observers' detection thresholds.…”